The present invention relates to fiber reinforced polymer composite materials, and more particularly pertains to an integrally stiffened article formed from a fiber reinforced polymer composite material and a method of making the article.
Advanced composite structures which require high strength to weight ratios by means of stiffeners, spars, struts and trusses are produced by manufacturing individual sub-components which are then bonded together to form the macro-stiffened structure.
While each of the sub-components can be produced with optimal characteristics, the overall structure will only be as strong as the bonding between the various sub-components.
In accordance with the present invention, a technology has been devised in which the sub-component stiffeners, spars, trusses and struts share common fibers which join the various elements into a macro-structure which does not rely on bond strength of materials to integrate the stiffeners together into a macro structure.
As applied to a crank arm for bicycles, current materials of choice are aluminum or steel. While aluminum is light weight compared to steel, it does not have the modulus of steel and, as the crank is loaded, it flexes and energy is lost into the crank flex and not transmitted into the drive train. Steel has greater modulus than aluminum and transmits more energy into the drive train. Because steel is a heavier material than aluminum, more energy is expended by having to move the additional weight of the steel crank arm.
The integrally stiffened crank arm of the present invention is lighter weight than aluminum and steel, yet has stiffness and modulus greater than aluminum, approaching steel. This means the energy transference from the rider to the drive train of the bike through the crank arm is superior to aluminum because it doesn't flex as much as aluminum when it is loaded and is superior to steel because less energy is expended to move the crank arm due to its lighter weight.